To reduce the effects of contaminants on IC performance, a gettering layer, such as implanted phosphorus, may be added to the backside of the IC wafer. The gettering material traps impurities, such as sodium or metals, that diffuse within the wafer. To make the gettering layer effective, it is desirable that the gettering not be depleted, i.e., any electric field in the gettering layer is insufficient to substantially deplete at least a portion of the gettering layer of charges. Further, for the gettering to be effective, the gettering layer should not be isolated from any semiconductor portion of the IC wafer, such as by an insulating layer of silicon dioxide.
Bonded wafer technology, a form of dielectric isolation, poses a challenge to existing gettering technology. In a typical bonded wafer, active and passive devices are formed in a working semiconductor layer isolated by an insulating layer from a semiconductor layer which is used as a handle layer and give support to the working layer. However, placing a gettering layer on the handle layer is not effective to getter impurities in the working layer because of the insulating layer. Placing the gettering layer on the working layer may not be effective because there is a high likelyhood that portions of the gettering layer will be depleted.
Therefore, it is desirable to provide an effective gettering technique that is effective for bonded wafers or other dielectrically isolated wafer technologies.
Further, it is desirable to provide a single process for providing a effective getterer for bonding wafers or other dielectrically isolated wafer technologies.